class BaseIterator:
    """迭代器"""
    def __init__(self, data):
        self.__data = data
        self.toBegin()

    def toBegin(self):
        """将指针移至起始位置"""
        self.__curIdx = -1

    def toEnd(self):
        """将指针移至结尾位置"""
        self.__curIdx = len(self.__data)

    def next(self):
        """移动至下一个元素"""
        if(self.__curIdx < len(self.__data) - 1):
            self.__curIdx += 1
            return True
        else:
            self.__curIdx += 1
            return False

    def prevoius(self):
        """移动至上一个元素"""
        if(self.__curIdx > 0):
            self.__curIdx -= 1
            return True
        else:
            self.__curIdx -= 1
            return False

    def current(self):
        """获取当前的元素"""
        return self.__data[self.__curIdx] if (self.__curIdx < len(self.__data)) and self.__curIdx >= 0 else None



class NumberSequence:
    """生成一个间隔为step的数字系列"""
    def __init(self, init, step, max=100):
        self.__data = init
        self.__step = step
        self.__max = max

    def __iter__(self):
        return self

    def __next__(self):
        if(self.__data < self.__data + self.__step):
            temp = self.__data
            self.__data += self.__step
            return temp
        else:
            raise StopIteration


if __name__ == "__main__":
    print("从前往后遍历：")
    iterator = BaseIterator(range(10))
    while(iterator.next()):
        customer = iterator.current()
        print(customer, end="\t")
    print()
    print("从后往前遍历：")
    while(iterator.prevoius()):
        customer = iterator.current()
        print(customer, end="\t")
